The present invention relates to liquid crystal materials for use in electro-optic applications. More particularly, the present invention relates to liquid crystal/polymer composite materials, and methods and apparatus for the manufacture and application of such composite materials. Merely by way of example, the materials, methods and apparatus of the present invention are described with reference to a voltage imaging system. The materials, methods and apparatus of the present invention can be used with other electro-optic applications, for example liquid crystal composite materials used in flat panel displays.
Voltage imaging technology may be employed to detect and measure for defects in flat panel thin film transistor (TFT) arrays. According to this measurement technique, the performance of a TFT array is simulated as if it were assembled into a TFT cell and then the characteristics of the TFT array are measured by indirectly measuring actual voltage distribution on the panel, or so-called voltage imaging, using an electro-optic (EO) light modulator-based detector.
A voltage imaging system in its most basic form includes an electro-optic (EO) modulator, an imaging objective lens, a charge coupled device (CCD) camera or other appropriate or similar sensor, and an image processor. The electro-optic sensor of the EO modulator is based on the light scattering characteristics of liquid crystal (herein after “LC”) droplets in a polymer matrix, for example nematic liquid crystal droplets in a polymer matrix (liquid crystal/polymer composite, or LC/polymer) film. In operation, the EO modulator is placed approximately 5-35 microns above the surface of a thin film transistor (TFT) array, and a voltage bias is applied across a transparent electrode of a layer of indium tin oxide (ITO) on a surface of the EO modulator. Thereupon, the EO modulator capacitively couples to the TFT array so that an electric field associated with the TFT array is sensed by the liquid crystal/polymer composite layer. Intensity of incident light transmitted through the LC/polymer layer is varied, i.e., is modulated, by any variations in the electric field strength across the liquid crystal (LC) material in the liquid crystal/polymer composite material. This light is then reflected off a dielectric mirror and collected by the CCD camera or like sensor. A source of incident radiation, which may be for example infrared or visible light, is provided to illuminate the sandwich of TFT array, LC/polymer film and dielectric mirror.
Due to the close proximity of components relative to panels under test (PUT), LC/polymer modulator structures can be subject to damage in normal use by unwanted particles, which severely curtails useful life. Thus, modulator lifetime improvement can be one of the major objectives in LC/polymer modulator research and development.
Modulator sensitivity can be another important characteristic of an LC modulator device. Improved modulator sensitivity can lead to improved detection capability, and as such can be an important aspect of LC modulator development, in particular LC/polymer matrix research and development. In addition, some applications such as LC computer displays for notebooks can be sensitive to power consumption, such that improved sensitivity with lower voltages can lead to decreased power consumption and increased battery lifetime. Sensitivity for defect detection can be defined as the ratio of the change in transmitted light to the difference in voltage between a defective pixel and a good pixel on the TFT array.
Work in relation with the present invention suggests that current LC materials and the current manufacturing testing methods associated therewith, may be less than ideal. For example, particulate contamination can damage test apparatus, for example a voltage imaging system and/or the panel under test. Also, test apparatus sensitivity may be less than ideal.
While the above materials, apparatus and methods may be suitable for certain applications, there is a need in the art for improved electro-optic LC materials, more specifically improved-sensitivity and life-time performance of electro-optic LC materials and test apparatus.